1. Field of the Invention
The present invention generally relates to a mobile communication system, and more particularly, to a method and apparatus for efficiently processing Layer 2 (L2) control information included in a data unit.
2. Description of the Related Art
Universal Mobile Telecommunications System (UMTS) is a 3rd Generation (3G) asynchronous mobile communication system operating in Wideband Code Division Multiple Access (WCDMA), evolved from European mobile communication systems, Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS).
Long Term Evolution (LTE) is presently being considered a future-generation UMTS mobile communication system in the 3rd Generation Partnership Project (3GPP) working on the standardization of UMTS. LTE is a technology for realizing high-speed packet communications at or above 100 Mbps, aiming at deployment by 2010. To implement LTE, many techniques have been proposed, including reduction of the number of nodes residing on a communication path through simplification of a network configuration, and approximation of radio protocols as close to radio channels as possible.
FIG. 1 illustrates a configuration of an LTE mobile communication system.
Referring to FIG. 1, Evolved UMTS Radio Access Networks (E-RANs) 110 and 112 are of a simple 2-node structure including Evolved Node Bs (ENBs or Node Bs) 120, 122, 124, 126 and 128 and anchor nodes 130 and 132. A User Equipment (UE) 101 accesses an Internet Protocol (IP) network 114 via the E-RAN 110 or 112.
The ENBs 120, 122, 124, 126 and 128 correspond to conventional Node Bs of a UMTS system. They are connected wirelessly to the UE 101. Unlike the conventional Node Bs, the ENBs 120, 122, 124, 126 and 128 are complex in function. In the LTE system, all user traffic including real-time services like Voice over IP (VoIP) is serviced on a shared channel. Therefore, there is a need for an apparatus for collecting status information about UEs and scheduling them. The ENBs 120, 122, 124, 126 and 128 function as this apparatus.
As with High Speed Downlink Packet Access (HSDPA) or Enhanced uplink Dedicated CHannel (E-DCH), Hybrid Automatic Repeat reQuest (HARQ) is carried out between the ENBs 120, 122, 124, 126 and 128 and the UE 101. Yet, since a variety of Quality of Service (QoS) requirements are not satisfied simply with HARQ, an upper layer may perform an outer Automatic Repeat reQuest (ARQ). The outer ARQ also takes place between the UE 101 and the ENBs 120, 122, 124, 126 and 128.
To realize data rates of up to 100 Mbps, it is expected that Orthogonal Frequency Division Multiplexing (OFDM) with a bandwidth of 20 MHz will be used as a wireless access technology for LTE. Adaptive Modulation and Coding (AMC) will also be adopted, in which a modulation scheme and a channel-coding rate are decided adaptively according to the channel status of a UE.
Many future-generation mobile communication systems including LTE use both HARQ and ARQ as error correction techniques.
HARQ increases a reception success rate by soft-combining previous received data with retransmitted data without discarding the previous received data. Specifically, an HARQ receiver determines whether a received packet has errors. Depending on the presence or absence of errors, the HARQ receiver transmits a positive ACKnowledgment (HARQ ACK) signal or a Negative ACK (HARQ NACK) signal to an HARQ transmitter. The HARQ transmitter retransmits the HARQ packet when receiving the HARQ NACK signal and transmits a new packet when receiving the HARQ ACK signal. The HARQ receiver soft-combines the retransmitted packet with the previously received packet, thus decreasing an error probability.
ARQ is a scheme in which the receiver checks the Sequence Number (SN) of a received packet and requests retransmission of a packet that it has failed to receive. Compared to HARQ, ARQ does not soft-combine a previously received packet with a retransmitted packet.
In the LTE system, ARQ is performed by a Radio Link Control (RLC) protocol, i.e. an L2 protocol, whereas HARQ takes place in the Medium Access Control (MAC) layer or the physical layer. If RLC Protocol Data Units (PDUs) received from a MAC entity do not include RLC control information, an RLC reception (Rx) entity re-orders the RLC PDUs and performs a subsequent operation. If the RLC PDUs include RLC control information, the RLC Rx entity needs to process them efficiently. Accordingly, there exists a need for a technique for efficiently processing control information included in PDUs in a specific protocol layer such as the RLC layer.